package huawei;
/*
* @Author: wanghongfucoder
* @Date:   2017-06-27 10:38:27
* @Last Modified by:   wanghongfucoder
* @Last Modified time: 2017-06-27 10:57:24
*/

import java.util.Scanner;
public class Step {
    public static void main(String[] args) {
    	Scanner input = new Scanner(System.in);
    	int step=input.nextInt();
    	System.out.println(f(step));
    }

    public  static  int f(int n){
    	if (n==1) {
    		return 1;
    	}
    	if (n==2) {
    		return 2;
    	}
    	// f(n)=f(n-1)+f(n-2);
    	return f(n-1)+f(n-2);
    }
}